2PH9

Galanthamine bound to an ACh-binding Protein

Summary for 2PH9

• Entry DOI: 10.2210/pdb2ph9/pdb
• Related: 2PGZ
• Descriptor: Soluble acetylcholine receptor, (-)-GALANTHAMINE, TETRAETHYLENE GLYCOL, ... (4 entities in total)
• Functional Keywords: non-competitive inhibitors, nicotinic acetylcholine receptor, acetylcholine-binding protein, benzodiazepine, galanthamine, choline-binding protein
• Biological source: Aplysia californica (California sea hare)
• Total number of polymer chains: 5
• Total formula weight: 132404.17

Authors

Hansen, S.B.,Taylor, P. (deposition date: 2007-04-10, release date: 2007-07-03, Last modification date: 2024-10-09)

Primary citation

Hansen, S.B.,Taylor, P.
Galanthamine and non-competitive inhibitor binding to ACh-binding protein: evidence for a binding site on non-alpha-subunit interfaces of heteromeric neuronal nicotinic receptors.
J.Mol.Biol., 369:895-901, 2007

PubMed Abstract: Rapid neurotransmission is mediated through a superfamily of Cys-loop receptors that includes the nicotinic acetylcholine (nAChR), gamma-aminobutyric acid (GABA(A)), serotonin (5-HT(3)) and glycine receptors. A class of ligands, including galanthamine, local anesthetics and certain toxins, interact with nAChRs non-competitively. Suggested modes of action include blockade of the ion channel, modulation from undefined extracellular sites, stabilization of desensitized states, and association with annular or boundary lipid. Alignment of mammalian Cys-loop receptors shows aromatic residues, found in the acetylcholine or ligand-binding pocket of nAChRs, are conserved in all subunit interfaces of neuronal nAChRs, including those that are not formed by alpha subunits on the principal side of the transmitter binding site. The amino-terminal domain containing the ligand recognition site is homologous to the soluble acetylcholine-binding protein (AChBP) from mollusks, an established structural and functional surrogate. We assess ligand specificity and employ X-ray crystallography with AChBP to demonstrate ligand interactions at subunit interfaces lacking vicinal cysteines (i.e. the non-alpha subunit interfaces in nAChRs). Non-competitive nicotinic ligands bind AChBP with high affinity (K(d) 0.015-6 microM). We mutated the vicinal cysteine residues in loop C of AChBP to mimic the non-alpha subunit interfaces of neuronal nAChRs and other Cys loop receptors. Classical nicotinic agonists show a 10-40-fold reduction in binding affinity, whereas binding of ligands known to be non-competitive are not affected. X-ray structures of cocaine and galanthamine bound to AChBP (1.8 A and 2.9 A resolution, respectively) reveal interactions deep within the subunit interface and the absence of a contact surface with the tip of loop C. Hence, in addition to channel blocking, non-competitive interactions with heteromeric neuronal nAChR appear to occur at the non-alpha subunit interface, a site presumed to be similar to that of modulating benzodiazepines on GABA(A) receptors.

PubMed: 17481657
DOI: 10.1016/j.jmb.2007.03.067

Experimental method

X-RAY DIFFRACTION (2.88 Å)